Conversion of Diamino-Substituted Carbene Complexes into the

Treatment of cyclic diaminocarbene (M = Cr, Mo, W; m = 2, 3) with acylating agents resulted in the formation of the corresponding isocyanide complexes...
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Organometallics 1998, 17, 1937-1940

1937

Articles Conversion of Diamino-Substituted Carbene Complexes into the Isocyanide by Acylation Chi-Li Chen, Hung-Hui Lee, Tung-Ying Hsieh, Gene-Hsiang Lee, Shie-Ming Peng, and Shiuh-Tzung Liu* Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China Received June 12, 1997

Treatment of cyclic diaminocarbene complexes (CO)5M)CNH(CH2)mNH (1) (M ) Cr, Mo, W; m ) 2, 3) with acylating agents resulted in the formation of the corresponding isocyanide complexes (CO)5MCN(CH2)mNH2-n(COR)n (M ) Cr, Mo, W; m ) 2, 3; n ) 1, 2; R ) Ph CH3) in high yields. It appears that the N-acyl group destabilizes the diaminocarbene complexes and causes the cleavage of the C-N bond to form the isocyanide product. The reaction pathway leading to the isocyanide complexes is discussed. The crystal structure of (CO)5WCt N(CH2)2N(COPh)2 has been determined. Introduction Diamino-substituted carbene complexes have received much attention recently due to the discovery that nitrogen atoms direct carbene ligands to be good σ-donors, similar to phosphines.1- 8 Such carbene ligands are able to incorporate with various metal ions to form stable complexes.1-8 Indeed, the unusually stable palladium complex [MeNCHdCHN(Me)C]2PdI2 was found by Herrmann and co-workers to be a useful catalyst for the Heck reaction.3d However, the nitrogen-substituted carbenes of these studies are typically tertiary amines, few are secondary amine moiety.9 As mentioned, the better (1) Regitz, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 725 and references therein. (2) (a) Arduengo, A., J. III; Goerlich, J. R.; Marshall, W. J. J. Am. Chem. Soc. 1995, 117, 7, 11027. (b) Alder, R. W.; Allen, P. R.; Murray, M.; Orpen, A. G. Angew. Chem., Int. Ed. Engl. 1996, 35, 5, 1121. (c) Enders, D.; Breuer, K.; Raabe, G.; Runsink, J.; Teles, J. H.; Melder, J.-P.; Ebel, K.; Brode, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 4, 1021 and references therein. (3) (a) Herrmann, W. A.; Elison, M.; Fischer, J.; Ko¨cher, C.; Artus, G. R. Chem. Eur. J. 1996, 2, 772. (b) O ¨ fele, K.; Herrmann, W. A.; Mihalios, D.; Elison, M.; Herdtweck, E.; Scherer, W.; Mink, J. J. Organomet. Chem. 1993, 459, 177. (c) Herrmann, W. A.; Gerstberger, G.; Spiegler, M. Organometallics 1997, 16, 2209. (d) Herrmann, W. A.; Elison, M.; Fischer, J.; Ko¨cher, C.; Artus, G. R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 4, 2371 and references therein. (4) Enders, D.; Gielen, H.; Raabe, G.; Runsink, J.; Teles, J. H. Chem. Ber. 1996, 129, 1483. (5) Kuhn, N.; Bohnen, H.; Fahl, J.; Bla¨ser, D.; Boese, R. Chem. Ber. 1996, 129, 1579. (6) Kernbach, U.; Ramm, M.; Luger, P.; Fehlhammer, W. P. Angew. Chem., Int. Ed. Engl. 1996, 35, 310. (7) Taton, T. A.; Chen, P. Angew. Chem., Int. Ed. Engl. 1996, 35, 1011. (8) Guerret, O.; Sole´, S.; Gornitzka, H.; Teichert, M.; Trinquier, G.; Bertrand, G. J. Am. Chem. Soc. 1997, 119, 6668. (9) (a) Michelin, R. A.; Zanotto, L.; Braga, D.; Sabatino, P.; Angelici, R. J. Inorg. Chem. 1988, 27, 93. (b) Fehlhammer, W. P.; Zinner, G.; Bakola-Christianopoulou, M. J. Organomet. Chem. 1987, 331, 193. (c) Belluco, U.; Michelin, R. A.; Ros, R.; Bertani, R.; Facchin, G.; Mozzon, M.; Zanotto, L. Inorg. Chim. Acta 1992, 200, 883. (d) Sabate´, R.; Schick, U.; Moreto´, J. M.; Ricart, S. Organometallics 1996, 15, 3611 and references therein.

the donor nitrogen, the stronger the metal-carbon bond in the related metal complexes. Thus, electronic modification of the donor character of the nitrogen substitutents in order to weaken the metal-carbon bonds becomes an interesting prospect. It has been reported by Do¨tz and co-workers that the N-acylated products of (CO)5CrdC(NHR)R′ have better reactivities toward alkynes in annelation reactions.10 As part of our studies on the properties of metal carbene complexes, we have prepared the cyclic diamino-substituted carbene complex 1 which holds secondary amine moieties.11 In view of the modification of the secondary amine functionality, we report that isocyanide complexes are formed instead of N-acylated carbene species when diaminocarbene 1 is reacted with acylating agents.

Results and Discussion The reaction of 1c with an excess of benzoyl chloride in the presence of pyridine at 100 °C did not provide the N-acylated carbene product as expected. Instead, the isocyanide tungsten complex 2c was obtained in 92% yield. The isocyanide complex was characterized by both spectroscopic and elemental analyses. The infrared spectrum of 2c in dichloromethane clearly shows the carbonyl and isocyanide functionalities of the molecule. Thus absorptions at 2174 (w), at 2068 (w) and 1948 (s), and at 1697 and 1660 (s) cm-1 are consistent with the coordinated isocyanide, the pentacabonyltungsten and the amidocarbonyl moieties. Both the 1H and 13C NMR spectra are also in agreement with the proposed structure. Finally, the composition of 2c is confirmed by X-ray single-crystal determination (see crystallography).

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Table 1. Spectral Data of Isocyanide Complexes isolated compd yield (%) sCtN 2a 2b 2c 2d 3a 3c 4a 4b

77 48 92 80 51b 33b 52 51

2169 2169 2174 2177 2171 2177 2165 2181

IR (cm-1) 13C NMR MsCtO NsC(dO)R δCN, (ppm)a 2066, 1944 2070, 1959 2068, 1948 2070, 1945 2061, 1945 2066, 1945 2067, 1942 2071, 1936

1700, 1658 1699, 1658 1697, 1660 1684, 1653 1646, 1640, 1720, 1708 1720, 1678

Scheme 1. Possible Mechanism for the Formation of Isocyanide Complexes

166.0 155.2 145.6 146.7 163.5 144.8 145.9 144.0

a Due to the weak intensity and broadening of the peak, the values of JW-C are not available. b Accompanied with the formation of 2a (25%) or 2c (20%).

Under the same conditions, both the chromium and molybdenum carbene complexes (1b and 1c) yielded their corresponding isocyanide complexes (eq 1). In

addition, cyclic diaminocarbene in different ring sizes, such as 1d, proceeded under the same type of reaction to yield 2d. We also tried to prepare the monoacylated product, but we found that a mixture of monobenzoylated amidoisocyanide complexes 3 and 2 (ca 2:1 ratio) was obtained from the reaction of an equimolar amount of carbene and acylating agent at the temperature of refluxing a tetrahydrofuran solution. Other acylating agents under various conditions also provide the corresponding N-acylated isocyanide complexes. Treatment of 1c and 1d with an excess of acetic anhydride in the presence of sulfuric acid or acetyl chloride in the presence of pyridine produced 4a and 4b, respectively.

Some of the spectral data of these complexes are summarized in Table 1. It is reported by Do¨tz and co-workers that aminocarbene chromium complexes [(CO)5CrdC(R)NHR] readily underwent acylation with acetic anhydride or di-tertbutyl dicarbonate in the presence of 4-(N,N-dimethylamino)pyridine at 25 °C.10 Diamino-substituted carbenes, however, do not react with acyl chloride under mild conditions, which is attributed to the high stability of such complexes. But at elevated temperatures, the acylation proceeds, followed by the cleavage of the C-N bond to form the isocyanide complex. In our previous investigation, we were able to obtain the N-alkylated products 5 by the deprotonation of 1 with NaH followed by treatment with various alkyl iodides.11 By adopting a similar strategy, the dianion 6 was prepared by the treatment of 1d with 2 equiv of (10) (a) Do¨tz, K. H.; Grotjahn, D.; Harms, K. Angew. Chem., Int. Ed. Engl. 1989, 28, 1384. (b) Grotjahn, D. B.; Kroll, F. E. K.; Scha¨fer, T.; Harms, K.; Do¨tz, K. H. Organometallics 1992, 11, 298. (11) Liu, C.-Y.; Chen, D.-Y.; Cheng, M.-C.; Peng, S.-M.; Liu, S.-T. Organometallics 1996, 15, 1055.

n-butyllithium in tetrahydrofuran at - 78 °C. Followed by addition of an excess of acetyl chloride to the dianion solution, the reaction mixture was allowed to warm to room temperature slowly. Monitoring the acylation by NMR spectroscopy reveals that the reaction took place at - 20 °C, but the observed outcome is the isocyanide product. None of the N-acylated carbene species 7 was detected by NMR. As a control run, the reaction of 6 with methyl iodide was carried out under similar conditions, which provided the methylated product 8 exclusively. This indicates that the first N-acylation takes

place prior to the cleavage of the C-N bond. Such an acylation also results in the immediate cleavage of the C-N bond to provide the isocyanide product. A possible mechanism for the formation of isocyanide complexes from the carbenes is illustrated in Scheme 1. The carbenes undergo N-acylation first to yield the intermediate 7. The amido group decreases the stability of the aminocarbene dramatically, which causes the ring-opening reaction that leads to the isocyanide complex. It is noted by Aumann and co-workers that reaction of aminocarbene (CO)5CrdC(NH2)R with R′CHO in the presence of base yields a mixture of a 2-azaallenyl complex and an isocyanide complex (CO)5CrCN-R 10.12 The formation of 10 is clearly involved in the migration of the substituent. In our investigation, the isocyanide complexes are simply created via the cleavage of C-N bonds and the driving force is presumably due to the electronic destabilization of the amido group toward the carbene functionality and the relief of the steric interaction between the substituted cyclic carbene constituent and the carbonyl ligands. Crystallography The data for the crystal of complex 2c is summarized in Table 2, and the ORTEP plot of 2c is depicted in Figure 1. As expected, the tungsten metal ion displays a typical octahedral geometry with the isocyanide donor and five carbonyl ligands. All bond distances and angles lie within normal ranges, as given in Table 3. The distance of the metal to isocyanide ligand (W-C6 2.10(12) Aumann, R.; Althaus, S.; Kru¨ger, C.; Betz, P. Chem. Ber. 1989, 122, 357.

Diamino-Substituted Carbene Complexes Table 2. Crystal Data, Collection, and Refinement Details for Complex 2c formula cryst size, mm cryst syst space group a, Å b, Å c, Å β, deg Z V, Å3 Dcalcd, gcm-3 µ, cm-1 radiation temp, K F(000) diffractometer scan type scan width, deg hkl ranges scan speed (deg/min) no. of reflns measd no. of reflns obsd (I > 2.0 σ(I)) no. of params refined refinement program Rf, Rwa GOF resid in final D-map, e Å-3

C22H14N2O7W 0.30 × 0.50 × 0.50 monoclinic P21/c 11.591(3) 25.520(5) 7.701(5) 96.21(5) 4 2264.5 (16) 1.766 52.513 Mo KR (0.7107 Å) 298 1156 Enraf-Nonius CAD 4 θ-2θ 2(0.70 + 0.35 tan θ) -13 to 13, 0-30, 0-9 2.75-8.24 3871 2768 290 NRCVAX 0.056; 0.064 2.15 -2.620 and 2.110

aR ) ∑(F - F )/∑(F ); R ) [∑(w(F - F ))2/∑(wF 2)]1/2. GOF f o c o w o c o ) [∑(w(Fo - Fc))2/(no. of reflns - no. of params)]1/2.

Figure 1. ORTEP plot of 2c.

(2) Å) is identical to that of the species CH3C[CH2NCW(CO)5]3 (9; 2.08(2) Å) reported by Hahn and co-workers.13 Due to the isoelectronic nature of the isocyanide and carbonyl ligands, the distances between the metal and carbonyl ligands either cis or trans to the isocyanide are essentially indistinguishable, which is similar in the structure of 9. Apparently, there is not much of a trans influence in this kind of structure. The bond length of C6-N1 (1.17(2) Å) is typical for CtN in the coordinated isocyanide ligand, which is consistent with the spectral data for this functionality. Summary It has been demonstrated in this report that the stable diaminocarbene ligand can be converted into the isocyanide complex via the cleavage of the C-N bond. Along with this, it is also found that the mono-N-alkylated diaminocarbene (CO)5WCN(Et)CH2CH2NH does not react with benzoyl chloride in the presence of pyridine in refluxing tetrahydrofuran. This appears that (13) Hahn, F. E.; Tamm, M. J. Organomet. Chem. 1991, 410, C9.

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formation of the N-acylated diaminocarbene complexes is a challenge. We are currently working on developing the synethetic approach to the N-acylated diaminocarbene complexes. Experimental Section General Information. Nuclear magnetic resonance spectra were recorded in CDCl3 on either a Bruker AC-E 200 or AM-300 spectrometer. Infrared spectra were measured on a Biorad FT-30 instrument in CH2Cl2 solution, unless otherwise stated. All of the reaction, manipulation, and purification steps were performed under a dry nitrogen atmosphere. Tetrahydrofuran was distilled under nitrogen from sodium benzophenone ketyl. Dichloromethane was dried by CaH2 and then distilled under nitrogen. Pyridine was dried over sodium hydroxide and distilled before use. Other chemicals and solvents were used from commercial sources without further purification. Complexes 1a-d were prepared by the method previously reported.11 General Procedure of the Acylation of 1a-c. A mixture of 1 (0.1 mmol), benzoyl chloride (0.3 mmol), and pyridine (5 mL) was heated at 100 °C for 8-10 h. After the reaction mixture was cooled to room temperature, it was poured into water (20 mL) and extracted with dichloromethane. The organic portion was separated, washed with water, dried over MgSO4, and concentrated. The residue was chromatographed on silica gel with ethyl acetate/hexane (1:4) as the eluent. After concentration of the elute, the isocyanide complex was obtained. (CO)5WCN(CH2)2N(COPh)2 (2c). Into a flask equipped with a refluxing condenser were placed 1c (1.0 g, 2.54 mmol), benzoyl chloride (0.9 mL, 7.81 mmol), and pyridine (5 mL). The resulting mixture was heated at 100 °C for 8 h. Water (20 mL) followed by dichloromethane (25 mL) were added to the reaction mixture. The organic layer was separated, dried, and concentrated. The residue was chromatographed on silica gel (60 g) with ethyl acetate/hexane (1:4) as the eluent. Complex 2c was obtained as a white solid (1.16 g, 92%). Recrystallization from a solution of dichloromethane and hexane gave 2c as a clear, colorless crystalline solid that is suitable for X-ray crystal determination. Complex 2c: white solid; mp 142-144 °C (dec); IR 2174 (υCtN), 2068, 1948 (υCO), 1697, 1660 cm-1 (υN-CO); 1H NMR (200 MHz) δ 7.4-7.0 (m, 10 H, Ar-H), 4.44 (t, J ) 6 Hz, 2 H), 4.16 (t, J ) 6.0 Hz, 2 H); 13 C NMR (CDCl3, 50 MHz) δ 195.8, 194.0 (JW-C ) 60 Hz), 173.7, 145.6 (-CtN-), 135.8, 132.3, 128.9, 128.3, 45.0, 43.2. Anal. Calcd for C22H14N2O7W: C, 43.88; H, 2.34; N, 4.65. Found: C, 44.14; H, 2.33; N, 4.60. (CO)5CrCN(CH2)2N(COPh)2 (2a): white solid (77%), mp 150-151 °C (dec); IR 2169 (υCtN), 2066, 1944 (υCO), 1700, 1658 cm-1 (υN-CO); 1H NMR (200 MHz) δ 7.40-7.11 (m, 10 H, ArH), 4.40 (t, J ) 6.0 Hz, 2 H), 4.07 (t, J ) 6.0 Hz, 2 H); 13C NMR δ 216.6, 214.5 (Cr-CO), 173.7, 166.0 (-CtN-), 135.8, 132.2, 128.8, 128.3, 45.0, 43.4. Anal. Calcd for C22H14N2O7Cr: C, 56.18; H, 3.00; N, 5.96. Found: C, 55.92; H, 2.94; N, 5.88. (CO)5MoCN(CH2)2N(COPh)2 (2b): white solid (48%), mp 133-134 °C (dec); IR 2169 (υCtN), 2070, 1959 (υCO), 1699, 1658 cm1 (υN-CO); 1H NMR (200 MHz) δ 7.41-7.09 (m, 10 H, ArH), 4.41 (t, J ) 6.0 Hz, 2 H), 4.09 (t, J ) 6.0 Hz, 2 H); 13C NMR δ 206.4, 203.5 (Mo-CO), 173.7, 155.2 (-CtN-), 135.8, 132.2, 128.8, 128.2, 45.0, 43.0. Anal. Calcd for C22H14N2O7Mo: C, 51.38; H, 2.74; N, 5.45. Found: C, 50.86; H, 2.75; N, 5.31. (CO)5WCN(CH2)3N(COPh)2 (2d): white solid (80%), IR 2177 (υCtN), 2070, 1945 (υCO), 1684, 1653 cm-1 (υN-CO); 1H NMR (300 MHz) δ 7.41-7.11 (m, 10 H, Ar-H), 4.18 (t, J ) 6.6 Hz, 2 H), 3.84 (t, J ) 6.6 Hz, 2 H), 2.26 (pent, J ) 6.6 Hz, 2 H); 13C NMR δ 196.2, 194.3 (J W-C ) 62 Hz), 174.0, 146.7

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Table 3. Selected Bond Distances (Å) and Angles (deg) W-C1 W-C2 W-C3 W-C4 C6-W-C1 C6-W-C2

1.93(2) 2.06(2) 1.97(2) 1.97(2) 88.5(7) 91.6(6)

C1-O1 C2-O2 C3-O3 C4-O4 C6-W-C3 C6-W-C4

1.22(3) 1.12(3) 1.16(2) 1.18(2) 177.1(8) 89.1(6)

(-CtN-), 136.0, 132.1, 128.8, 128.3, 43.8, 42.2, 28.9. Anal. Calcd for C23H16N2O7W: C, 44.83; H, 2.62; N, 4.55. Found: C, 44.44; H, 2.72; N, 4.42. (CO)5CrCN(CH2)2NH(COPh) (3a). To a flask was added 1a (0.2 g, 0.76 mmol), C6H5COCl (0.22 mL, 1.9 mmol), and pyridine (0.15 mL, 2.48 mmol) in tetrahydrofuran (5 mL). The mixture was heated to reflux for 30 h. After the reaction mixture was cooled to room temperature, it was washed with water and the organic layer was separated. The organic extract was dried and concentrated. The residue was chromatographed on silica gel with ethyl acetate/hexane (1:4) as the eluent. Two fractions were collected and concentrated, which were identified as 2a (25%) and 3a (51%). Complex 3a was obtained as a white solid: mp 112-113 oC (dec); IR 3358 (υN-H) 2171 (υCtN); 2061, 1945 (υCO) 1646 cm1 (υN-CO); 1H NMR (200 MHz) δ 7.79-7.76 (m, 2 H, Ar-H), 7.57-7.40 (m, 3 H, Ar-H), 6.5 (br, 1H, N-H), 3.89 (t, J ) 6 Hz, 2 H), 3.76 (t, J ) 6.0 Hz, 2 H); 13C NMR δ 216.6, 214.7 (Cr-CO), 168.2, 163.5 (-CtN-), 133.3, 132.0, 128.7, 126.9, 44.1, 39.3. Anal. Calcd for C15H10N2O6Cr: C, 49.19; H, 2.75; N, 7.65. Found: C, 49.21; H, 2.92; N. 7.59. (CO)5WCN(CH2)2NH(COPh) (3c). The preparation of 3c was similar to the procedure described for 3a. Complex 3c is a light-yellow solid (33%); mp: 131-132 °C (dec); IR 3363 (υN-H), 2177 (υCtN), 2066, 1945 (υCO), 1640 cm1 (υN-CO);1H NMR (CDCl3, 200 MHz) δ 7.76 (m, 2 H), 7.54-7.40 (m, 3 H), 6.74 (br, 1 H), 3.93 (m, 2 H), 3.74 (m, 2 H); 13C NMR (CDCl3, 50 MHz) δ 195.8, 194.2 (JW-C ) 62 Hz), 168.1, 144.8 (-CtN-), 133.2, 132.2, 128.8, 129.9, 44.0, 39.3. Anal. Calcd for C15H10N2O6W: C, 36.17; H, 2.62; N, 5.62. Found: C, 35.92 H, 2.14; N, 5.53. (CO)5WCN(CH2)2N(COCH3)2 (4a). To a mixture of complex 1c (2.0 g, 5.07 mmol) and acetic anhydride (10 g, 98 mmol) was added a few drops of concentrated sulfuric acid. The resulting mixture was heated at reflux for 12 h. After concentration under vacuum, the residue was chromatographed on silica gel (ethyl acetate/hexane, 1:4). Upon concentration,

W-C5 W-C6 N1-C7 C6-W-C5 W-C6-N1

2.08(2) 2.10(2) 1.42(2)

C5-O5 C6-N1

89.0(6) 178(2)

C6-N1-C7

1.08(3) 1.17(2)

176(2)

complex 4a was obtained as a light yellow solid (1.26 g, 52%): mp 60-62 °C (dec); IR 2165 (υCtN), 2067, 1943 (υCO), 1720, 1708 cm-1 (υN-CO); 1H NMR (200 MHz) δ 4.04-3.98 (m, 4 H), 2.47 (s, 6 H); 13C NMR (CDCl3, 50 MHz) δ 195.4, 193.8 (JW-C ) 63 Hz), 172.5 (Me-CO-), 145.9 (-CtN), 43.4, 42.9, 26.4. Anal. Calcd for C12H10N2O7W: C, 36.17; H, 2.62; N, 5.62. Found: C, 35.92 H; 2.14; N, 5.53. (CO)5WCN(CH2)3N(COCH3)2 (4b). This compound was prepared similarly to 4a and isolated as a white solid (51%): IR 2181 (υCtN), 2071, 1936 (υCO), 1720, 1678 cm-1 (υN-CO); 1H NMR (300 MHz) δ 3.81 (t, J ) 7 Hz, 2 H), 3.74 (t, J ) 7 Hz, 2 H), 2.42 (s, 6 H), 2.03 (m, 2 H); 13C NMR δ 195.8, 194.1 (JW-C ) 63 Hz), 172.8, 144.0 (-CtN-), 42.1, 42.0, 28.8, 26.3. Anal. Calcd for C13H12N2O7W: C, 31.73; H, 2.46; N, 5.69. Found: C, 32.44; H, 2.42; N, 5.44. Crystallography. Cell parameters were determined on a CAD-4 diffractometer at 298 K by a least-squares treatment. Atomic scattering factors were taken from ref 14. Calculations were performed using the NRCC SDP VAX package.15 The crystal data is listed in Table 2, and selected bond distances and angles are summarized in Table 3. The atomic coordinates as well as other crystal data are collected as Supporting Information.

Acknowledgment. We thank the National Science Council (Grant No. NSC86-2113-M002-21) for financial support. Supporting Information Available: Tables listing atomic coordinates, anisotropic thermal parameters, and complete bond distances and bond angles for 2c (3 pages). Ordering information is given on any current masthead page. OM970500+ (14) International Tables for X-ray Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV. (15) Gabe, E. J.; Lee, F. L. Acta Crystallogr., Sect. A 1981, 37, S339.